#!/bin/bash
a="abc"
b="efg"

if [ $a = $b ]
then
	   echo "$a = $b : a 等于 b"
   else
	      echo "$a = $b: a 不等于 b"
      fi
      if [ $a != $b ]
      then
	         echo "$a != $b : a 不等于 b"
	 else
		    echo "$a != $b: a 等于 b"
	    fi
	    if [ -z $a ]
	    then
		       echo "-z $a : 字符串长度为 0"
	       else
		          echo "-z $a : 字符串长度不为 0"
		  fi
		  if [ -n "$a" ]
		  then
			     echo "-n $a : 字符串长度不为 0"
		     else
			        echo "-n $a : 字符串长度为 0"
			fi
			if [ $a ]
			then
				   echo "$a : 字符串不为空"
			   else
				      echo "$a : 字符串为空"
			      fi
